In cellular radio communication systems radio transmission are typically subject to power control. Thus in e.g. cellular radio communication systems conforming to the 3rd Generation Partnership Project (3GPP) Universal Mobile Telecommunications (UMTS) specifications, power control of radio transmissions are performed utilizing both inner and outer-loop power control functions.
The inner-loop power control (ILPC) adjusts the transmit power of a sending entity towards a specific signal quality target, e.g. signal-to-interference ratio (SIR) target, at a receiving entity, whereas the outer-loop power control (OLPC) adjusts the signal quality target of the inner loop power control in order to maintain a specified communication quality-based target (e.g. Block Error Rate (BLER) or number of transmission attempts). In the uplink direction, i.e. from mobile station to base station, OLPC is used both in connection with DCH (Dedicated Channel) and E-DCH (Enhanced Data Channel) transport channels, but typically in a slightly different manner. Due to the use of HARQ (Hybrid Automatic Repeat Request) protocol in EUL (Enhanced Uplink), i.e. when communicating using an E-DCH transport channel, the OLPC quality target is typically the number of transmission attempts while for communications using a DCH transport channel, the OLPC quality target is typically Block Error Rate (BLER).
The transmission format, the so called E-DCH Transport Format Combination (E-TFC), used in each Transmission Time Interval (TTI) can be varied between TTIs so as to adapt the amount of data transmitted to the currently available resources and/or the amount of data available for transmission.